ISAS succeeded in deploying a big thin film for solar sail in space for the first time in the world.
ISAS launched a small rocket S-310-34 from Uchinoura Space Center in Kagoshima, Japan, at 15:15, August 9, 2004 (Japan Standard Time). The launch was the culmination of a historic new technology, the world-first successful full-fledged deployment of big films for solar sail.
A solar sail is a spacecraft without a rocket engine. It is pushed along directly by light particles from the Sun, reflecting off its giant sails. Because it carries no fuel and keeps accelerating over almost unlimited distances, it is the only technology now in existence that can one day take us to the stars.
Although both scientists and science-fiction authors have long foreseen it, no solar sail has ever been launched until now. It is because superlight material for thin film which could bear extremely critical environment in space. Now due to the development of material and production technology, we can utilize promising film materials for solar sail, and the experimental deployment trials toward realization of solar sail have been initiated in some countries.
The S-310 rocket which was launched from Uchinoura Space Center at 15:15 of August 9, 2004, carried two kinds of deploying schemes of films with 7.5 micrometers thickness. A clover type deployment was started at 100 seconds after liftoff at 122 km altitude, and a fan type deployment was started at 169 km altitude at 230 seconds after liftoff, following the jettison of clover type system. Both experiments of two types deployment were successful, and the rocket splashed on the sea at about 400 seconds after liftoff.

Hell's bells! Us Americans are trying to figure out how to get back to the Moon, and the Japanese are laying the groundwork for cheap (albeit slow) interstellar (or at least interplanetary) exploration/colonization!

Ekkehard:

1. Yes; they work by reflecting EM radiation. If you can make 'em reflective to UV Radiation and higher, you get even more power.

2. No, because the solar sail pulls the vehicle along behind it. Think of a parachute being blown along by the wind: the sucker strapped into the chute gets dragged along behind.

3. Hell yes, but they're really lousy with the acceleration (think a couple of miles a day acceleration), and really good with top speed (186,000mi/s). So they're great for really long hauls moving outward from the Sun. If you're trying to bring something in (say chemicals from one of the gas giants), though, you need some form of braking device: a solar sail can only speed up (it's only reflective on the windward [back] side -- if it was reflective on the leeward [front] side, it'd collapse under the impact of the Sunlight).

For these reasons, I still stick by the idea of the fusion drive: acceleration's great, top speed isn't as good (but if you're in a single system, you don't really need it anyway), and you can stop simply by standing the bird on its tailpipe.

This should answer Ekkehard’s 3rd question as well, Cosmos1 is a private solar sail designed to be fully working, not just a model or a test vehicle. It is funded by the Planetary Society, a powerful pro-space lobby group and they are being helped by Russian scientists.

I sympathise with the fusion drive thing Spacecowboy, but since sustainable fusion has not yet been achieved on earth I think solar sails are the solution for the here and now.

what prevents pushing the vehicle by a solar sail instead of pulling it? Is there a differnece in the forces working or in the energy needed? And is it waste of material if the film is used as radiation shield only? Or doesn't it work then?

Concerning my third quetsion I thought of braking in orbit before reentry. The solar sail might be kept folded together until braking is desired. Then in might be unfolded and special mirror-based telescopes might focus sun light to the sail or a laser beam is directed to it.

Sounds utopic to me but even because of this I want to ask: What size or amount of telescope might be required? What energy is required for the laser? It seems to me that focusing shouldn't bundle the light to a point but increase the amount of light shing onto the surface of the sail. The lasr beam should have a sufficient diameter too.

Is something like this possible? If yes this would be a solution to remove the requirement of propellant for deceleration and of atmospheric braking.

You could brake with a solar sail if you're moving toward the sun. It'd act just like the parachute. So you could conceiveably attach a solarsail to a big asteroid, accellerate it out further towards another planet like jupiter, fold up sail, use the gravity well, to swing it back towards earth, unfurl the sail again, only this time behind, and use the sunlight pressure to brake the asteroid into Earth/moon orbit for use as you please.

Yes - it seems to be possible right now without a telescope or a laser if it is an interplanetary travel as you described and the velocity combined to such travels.

But does work in normal Low Earth Orbit what I described? Velocity is much less than in the case of interplanetary travel. The distance available for braking by solar sail is much less too. I really thought of braking a small orbital spacecraft as discussed by Burt and Dick Rutan in one of the articles under www.xprizenews.org.

I wonder if solar sails could be used in conjunction with an ion propulsion system, utilizing all that surface area of the sail to also power the ion drive.

No joy. In order for a solar sail to be efficient, it has to be insanely light weight, and extremely reflective. Current designs use atom-thin aluminum sheet backed by a super-light-absorbent surface (like black felt, except lighter). A photocell is inherently light-absorbent, and thus useless as a sail (and the backing is facing outwards, where there's almost no light for the cell to gather.

Ekkehard Augustin wrote:

Yes - it seems to be possible right now without a telescope or a laser if it is an interplanetary travel as you described and the velocity combined to such travels.

But does work in normal Low Earth Orbit what I described? Velocity is much less than in the case of interplanetary travel. The distance available for braking by solar sail is much less too. I really thought of braking a small orbital spacecraft as discussed by Burt and Dick Rutan in one of the articles under www.xprizenews.org.

Well, telescopes are useless, but lasers (done very carefully so that they're properly unfocused at the right distance) can come in handy for giving and acceleration boost. The kind of laser required would use up the entire world's energy supply for a year for a burst of a few seconds, though. Fusion or at least very serious fission power is required for a laser of that magnitude.

In answer to your last two questions, no. Solar sails are great for long hauls, but are practically useless for short runs, due to their atrocious acceleration. For operations around a single planet, some form of rocket is the ideal solution.

The laser is proving to be not only to be utopic but nonsense too based on the comparison of required energy to entire world's energy supply for a year.

But what is the basis of the pole sitter idea I read of a few years ago? The idea was to use light sails to establish satellites above the poles ("Global Observations and Alerts from Lagrange-Point, Pole-Sitter, and Geosynchronous Orbits (GOAL&GO)" at the NIAC Homepage - I didn't read all).

Is that possible?

If yes this would mean that the natural sun light in space is able to work against gravity if the object to be hold doesn't move relative to earth. At any moved object in orbit sun light doesn't have any observable effect. So there must be a break-even-velocity at which sun light might help braking the object. As I read in another NIAC-study the effect of the solar light depends on the area of the sail. The study is considering realistic a sail of 1 square-km and a few nanometers thickness. This sail would carry a nanosat probe to alpha centauri within 32 years if started at 3 million to 4,5 million km distance from the sun. Nanosat is considered to have a mass of 10 kilograms.

Is the pole sitter possible and if yes what does that mean for private orbital spacecrfats?